Purification of crude aluminum

ABSTRACT

A process for purifying or upgrading crude aluminum by reacting sodium fluoride with a source of impure aluminum, e.g., an aluminum alloy, to obtain cryolite. The cryolite is then reacted with sodium metal to produce purified aluminum metal and sodium fluoride.

United States Patent [191 Becker et al.

[451 ]Dec.24, 1974 PURIFICATION OF CRUDE ALUMINUM Inventors: Warren E. Becker; James D.

Johnston, both of Baton Rouge, La.; Clarence L. Hildreth, Brookhaven, Miss.

Assignee: Ethyl Corporation, Richmond, Va.

Filed: Feb. 20, 1974 Appl. No.: 444,104

Related U.S. Application Data Continuation-impart of Ser. No. 234,401, March 13, 1972 which is a continuation-in-part of Ser. No. 878,951, Nov. 21, 1969, abandoned.

U.S. Cl 75/68 B Int. Cl .4 C22b 21/04 Field of Search 75/68 R, 68 A, 68 B References Cited UNITED STATES PATENTS 11/l984 Frishmuth 75/68 B 2,184,705 l2/l939 Willmore 75/68 B 2,607,675 8/1952 Gross 75/68 B X 3,397,056 8/l968 Layne et al. 75/68 B Primary ExaminerL. Dewayne Rutledge Assistant ExaminerM. J. Andrews Attorney, Agent, or FirmDonald L. Johnson; John F. Sieberth; Paul H. Leonard 10 Claims, No Drawings PURIFICATION OF CRUDE ALUMINUM CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Application Ser. No. 234,401, filed Mar. 13, 1972, which in turn is a continuation-in-part of Application Ser. No. 878,951, filed Nov. 21, 1969, both abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is in the field of metallurgy and broadly relates to the upgrading of aluminumcontaining materials by the reaction of a source of aluminum with sodium fluoride and to the utilization of this process in the chemical refining of various constituents of the aluminum-containing materials.

2. Description of the Prior Art Heretofore various methods have been described for the manufacture of aluminum metal. For example, a well-known process disclosed in U.S. Pat. No. 2,198,673 is that of preparing pure alumina from bauxite and subsequently effecting high temperature, molten state electrolysis of the alumina in a bath of molten cryolite. It is noteworthy that this process is character ized by the requirement of a special low silicon content bauxite for use in the initial stage of the process.

Another process disclosed in the foregoing patent is the subjection of a crude aluminum source material to a treating metal or alloy capable of forming with the aluminum an alloy which is comparatively rich in aluminum. This process is undertaken at relatively high temperature in a molten bath, and in a typical embodiment is characterized by treatment of an aluminumsilicon alloy with tin at about 500C to realize an aluminum product of 95.3 percent purity.

A method of refining and producing aluminum is disclosed in U.S. Pat. No. 2,184,705 and is essentially the disproportionation of monovalent aluminum compounds. In-this process impure aluminum and a halide are heated together at elevated temperature in an atmosphere effectively inert to aluminum to vaporize aluminum mono-halide therefrom which upon cooling disproportionates to aluminum and aluminum trihalide. The resulting vapors are condensed and the aluminum is separated from the condensate. Aluminum fluoride, alkaline earth fluorides and double fluorides containing aluminum are preferred. Subsequent work by another inventor as disclosed in U.S. Pat. No. 3,397,056 teaches that this aluminum fluoride process works only if low levels of impurities are present in the aluminum. This later work shows that this earlier process was ineffective when aluminum containing 35 percent impurities was used.

Another method of chemically refining aluminum is disclosed in U.S. Pat. No. 2,513,339. The technique of this disclosure includes utilizing certain relatively volatile metals to entrain aluminum vapors by passing the vapors of these metals over or through a molten bath of aluminum or aluminum alloy. Condensation is used to separate the entrained aluminum from the entraining metallic vapors.

More recently, a technique for removing metallic aluminum from various alloys has been described in U.S. Pat. No. 3,102,805. This process is characterized by effecting the desired separation of aluminum from impurities in a medium in which the impurities are insoluble. The alloy is placed in this medium, which may be another metal, such as mercury, and the impurities are removed as solid material after the aluminum is dissolved. The aluminum is then separated from the dissolving medium by extraction.

A more recent process for separating aluminum from impure aluminum is described in U.S. Pat. No. 3,397,056. It is an aluminum fluoride process, but is a monofluoride one. Aluminum is recovered from its usual alloys and impure forms by heating in a reaction zone, at a pressure above about 100 mm. of mercury absolute, usually between about 100 mm. and 1.000 mm. of mercury absolute, a mixture of such impure aluminum source and a metal fluoride, e.g., sodium fluoride, potassium fluoride, calcium fluoride and magnesium fluoride along or in combination with aluminum fluoride to a temperature above the melting point of the mixture and below the boiling; point of the lowest boiling reactant at the pressure employed. Gaseous products are formed and these are passed from the reactor and are condensed in a quiescent zone. The liquid aluminum phase is allowed to separate from the molten metal fluoride phase and at least the aluminum phase is maintained in the liquid state. The phases are separated to produce a purified aluminum and metal fluoride. Aluminum mono fluoride is produced in the initial reaction and a sufficiently high temperature must be used to maintain the aluminum mono fluoride. A temperature or from C to 200C higher than the formation of the aluminum mono fluoride at the pressure employed is recommended. High temperatures of from about 1,300C to 1,750C are generally necessary. The lowest temperature reported was l,120C and this temperature did not produce satisfactory results.

It will be noted that all of the foregoing processes involve metallurgical or electrical techniques which frequently require elaborate and expensive equipment and necessitate close control of process conditions and reactant concentrations. Further, unlike chemical processes where stoichiometric amounts of product can frequently be realized, metallurgical and electrical processes for refining metals frequently require large quantities of reactants to produce a relatively small amount of product.

It is important in this regard to consider a chemical process for co-producing sodium and cryolite described in the Japanese Periodical Nippon Kinozoky Gakkai-Si 29 (5), 50l-500 (1965) at page 501. In this article the investigators found that pure aluminum metal would react with sodium fluoride to form sodium vapor and cryolite at reduced pressure and at a temperature ranging from 790C to 880C. Aluminum reacted to form cryolite in yields of up to about 40 percent.

The present invention is a distinct improvement over these prior art processes. Unexpectedly, the novel process of this invention can be carried out at substantially lower temperatures than those taught in U.S. Pat. No. 3,397,056.

SUMMARY OF THE INVENTION It has now been discovered that metallic aluminum can be refined in excellent yield from impure, aluminum-containing sources by application of a novel chemical process. The process is highly unique in that the aluminum reacted may be present in the form of substantially any impure, heretofore commercially useless source such as an alloy containing virtually any impurity.

Broadly, the invention relates to the reaction of sodium fluoride with such an aluminum source to form materials from which aluminum can be easily extracted. This discovery is significant as it would ordinarily be expected that certain impurities normally found in impure aluminum materials, such as silicon, titanium and iron, would react with the sodium fluoride to form compounds such as volatile silicon tetrafluoride. Unexpectedly it has been found that substantially all of these elements remain in the aluminum source material while the aluminum is selectively removed. Thus, the invention provides a useful method for producing purified aluminum metal from impure aluminum source materials.

In the present invention, sodium fluoride andan impure aluminum source are reacted at a relatively low temperature (about 850C-1,000C) under vacuum conditions to produce cryolite, sodium and pure aluminum. All of the products distill out of the reaction zone leaving behind impurities such as iron, silicon and titanium. Varying vapor pressures and differing distances of travel prior to condensing enable the products to be collected separately. The reaction does not reverse as the sodium and cryolite are not in physical contact with each other. Since vaporized sodium passes through the area of cryolite formation, a small amount of sodium may react with the cryolite. A partial reversal of the reaction may thus occur. Equipment can be varied as necessary to assure minimal reversal of the reaction. Subsequently, the sodium and cryolite are reacted at sufficient temperature (about 1,000C 1,300IC) and pressure (normal atmospheric or higher) to produce purified metallic aluminum and sodium fluoride. This latter reaction is well known and was used to commercially produce aluminum prior to the Hall process.

A further useful feature is the purification of aluminum-containing sources such as ferro-silicon and titanium alloys by selectively-removing the aluminum from these materials.

Accordingly, it is an important object of this invention to provide a process for the chemical refining of an impure aluminum-containing source by a simple chemical reaction between inexpensive and readily available chemical compounds and elements.

A further object is to provide a method of producing aluminum metal in excellent yield and purify from heretofore commercially useless aluminum alloys and scrap material.

Another object of this invention is to provide a method for chemically co-producing metallic sodium and cryolite, both products of which may be further utilized in the production of metallic aluminum.

A still further object is the purification of commerciallydesirable aluminum-containing source material exemplified by ferro-silicon and titanium alloys.

Other objects, features, advantages and characteristics of this invention will become more readily apparent from the ensuing description and appended claims.

DESCRIPTION OF THE PREFERRED EMBQDIMENT and at a temperature sufficiently high to distill sodium out of the reaction. A pressure of less than about 100 mm. of mercury is satisfactory with a pressure of 10 mm. or less of mercury being preferred. At these reduced pressures, a temperature of about 900C is preferred, and temperatures of from about 850C to about 1,000C are satisfactory. The reaction produces cryolite, sodium, aluminum and residue. The products, cryolite, sodium and aluminum are distilled out of the reaction zone leaving the impurities behind. The latter are usually iron, titanium and silicon. The products, having different vapor pressures and travelling different distances before condensing are vaporized or distilled out of the reaction zone and subsequently separately condensed and collected for future use. The aluminum is admixed with the cryolite. This reaction may be summarized as follows: I (1) 2 Alfimpurey 6 NaF Na AlF Residue 3 Na (pure) This first reaction is believed to take place in two steps as follows:

The initial products are sodium and aluminum trifluoride which recombine to form cryolite and aluminum metal. Aluminum monofluoride (AIF) is not a major intermediate because the ratio of A]:F atomsin the products of this invention is about 1:3. The ratio would have to be 1:] for AIF to be involved. The reaction does not reverse because the sodium and cryolite are not in physical contact with each other.

In the foregoing reaction or reactions, the cryolite is dium and cryolite is essential to effect the reaction.

Also, a vacuum should not be employed. A melt depressant such as calcium fluoride or other suitable metal halide maybe added to depress or lower the melting point of the cryolite. This latter or second reaction produces a liquid phase of sodium fluoride and a liquid phase of pure aluminum. Under certain reaction conditions a solid phase of sodium fluoride may be produced. Solid sodium fluoride can be separated from the liquid phase of pure aluminum without undue difficulty. The molten pure aluminum is readily tapped from the reactor and cast into suitable ingots or other desired shapes. This reaction is illustrated as follows:

2) 3 Na Na AlF 6 NaF Al In the foregoing process, substantially no aluminum mono fluoride is produced.

In carrying out the foregoing process, it may be desirable to include an intermediary step to enhance separation of the cryolite from the residue. In'such case, the cryolite and residue, which are solids, may be heated to a temperature sufficiently high to melt the cryolite. A temperature of about l,200C to about 1,300C is adequate. The molten cryolite may then be separated from the residue and subsequently reacted with sodium metal. This reaction is preferably effected at about 1,000 to 1,300C at a pressure at least as high as normal atmospheric pressure.

Conventional techniques for separating cryolite and residue may also be employed.

Alternative reaction equipment may be utilized while realizing essentially the same product. For example, two separate reaction zones may be used in the cryolite and metallic aluminum formation steps, respectively, or a single zone may be utilized. Further, the zone or zones may be located in equipment of varied design and capable of effecting either batch or continuous operation. In a preferred feature of this embodiment the cryolite is formed in a first zone, sodium metal is vaporized out of this zone and aluminum metal is formed in a second zone.

This embodiment of the invention is characterized by economy of operation in several aspects. First, in a preferred feature of operation sodium fluoride separated from the metallic aluminum formed in the last recovery step of the process is recycled to the initial sodium fluoride-impure aluminum reaction. In another preferred operational feature, metallic sodium vaporized out of a frist reaction zone in the first reaction step of this embodiment is recycled to a second reaction zone where it is reacted with cryolite.

A most preferred economical feature of the invention is the combination of the foregoing two operations. Additional convenience and ease of operation is presented by a feature wherein at least a portion of the cryolite recovered in the first recovery phase is vaporized out of the first reaction zone along with the vaporized sodium metal. This aspect of the invention allows easy collection of cryolite and sodium metal for subsequent use in producing aluminum metal or for disposition as co-products, an aspect of the invention which will be hereinafter further discussed. Thus, a most preferred combination ofthe foregoing operational expedients is the process where at least a part of the cryolite produced in the first reaction zone is carried out of that zone along with vaporized sodium metal, the sodium fluoride separated in the second recovery step is recycled to the impure aluminum-sodium fluoride reaction in the first reaction zone and the vaporized sodium metal produced in the first reaction zone and separated in the first recovery step is recycled to the aluminum metal producing step in the second reaction zone.

An important feature of the invention lies in the discovery that virtually all commercially useless impure aluminum sources such as alloys, intermetallic compositions and the like can be upgraded to substantially pure metallic aluminum by a comprehensive process in excellent yield. It is significant in this respect that successful utilization of the invention does not depend upon the relative solubilities of impurities present in various types of aluminum scrap materials as in the case in many metallurgical upgrading processes. Thus, the invention can be effectively applied to substantially any aluminum-containing source material regardless of the presence of constituents normally found in such sources such as copper, iron and the like. For example, an aluminum source composed of an aluminum- /aluminum-carbide/alumina mixture or an aluminum alloy containing titanium and appreciable quantites of iron and silicon or any one of these elements individually has been used successfully in practicing the inventive embodiments. Such an alloy may be one obtained by the carbothermic reduction of aluminum-containing ores and may contain not only one of these elements or a combination of all of them, but also substantially any other impurity and still provide a useful source of aluminum for application of the invention. Typically, the aluminum source material may have approximately the following composition by weight:

Aluminum 68% Silicon 27 Iron 3% Titanium While these composition percentages are not critical, the aluminum content should preferably be at least percent, and substantially any alloy or metallic scrap aluminum source, having at least this aluminum content will provide a suitable starting material for the embodiments of the invention regardless of the presence of impurites such as, or in addition to, those noted on the preceding page. In a typical carbothermic aluminum alloy source the silicon content may range from about 5 to about percent and the iron from about 0.1 to about 40 percent by weight of the alloy, while the aluminum content is at least 40 percent and the titanium content ranges from about 0.001 to about 10 percent by weight of the alloy.

In order to practice the invention with best advantage it has been found that the aluminum source may be introduced into the reaction system in relatively small chunks to facilitate a large surface area for interaction of the reactants. Aluminum may also be used in the form of turnings, powder, molten metal or any other convenient form. Size reduction may easily be accomplished by such processes as flaking, granulating, milling, or by any other conventional method known to those skilled in the art.

Depressants which may be used successfully in the invention are suitable inorganic salts of alkali metals and alkaline earth metals. A preferred depressant is calcium fluoride.

In a most preferred feature of the invention, the aluminum-containing source reacted with sodium fluoride contains, at least 40 percent by weight of aluminum, from about 5 to about 50 percent by weight of silicon, from about 0.1 to about 40 percent by weight of iron and from about 0.001 to about 10 percent by weight of titanium. Further, the reaction steps are effected in the presence of calcium fluoride at a temperature within the range of from about 700C to about 1,000C when the pressure is within the range of from about 10" to about 10" millimeters of mercury.

In general, the amount of reactants utilized in the invention are not critical. Thus, sodium fluoride may typically be added to the reaction zone along with the aluminum-containing source material in equal amounts. A more preferred ratio of alkali metal fluoride to impure aluminum is from about 1.5 to 1 to about 10 to l. A still more preferred range is from about 2 to 1 to about 5 to 1, and a most preferred fluoride .to aluminum source material ratio is about 3 to 1. Similarly, the amount of melting point depressant added to the reaction mixture is not critical, the quantity varying with the amount of alkali metal fluoride added to the system. It has been found that calcium fluoride and other alkali metal and alkaline earth metal fluorides may be used to successfully lower the melting point of the alkali metal fluoride when the ratio of sodium fluoride to melting point depressant is about 2 to 1.

In the metallic sodium addition phases of the invention, stoichiometric quantities of sodium may be used with good results. In the cryolite formation step a slight excess over stoichiometric quantites of sodium fluoride is preferred to ensure maximum utilization of aluminum in the impure aluminum source.

As heretofore noted, the invention is highly advantageous and novel in that several products can be produced, namely sodium metal and cryolite. The cryolite and sodium metal may be allowed to vaporize out of thereaction zone for easy recovery and may then be marketed or utilized as intermediates in the production of other useful chemical products/In a preferred feature of the invention cryolite and metallic sodium are coproduced by heating sodium fluoride with an aluminum-containing source having as a constituent (s) therein at least one of the elements silicon, iron and titanium. The reactants are heated in a reaction zone to an elevated temperature sufficient to form cryolite and to vaporize sodium metal out of the zone, but not high enough to thermally remove all of the elements originally present in the impure aluminum source material. Since recovery of cryolite and metallic sodium is easily effected by allowing at least a portion of both products to vaporize out of the cryolite-formation step of the process, this is a preferred method of operation. As previously noted, this aspect of the recovery operation is significant not only from the standpoint of easy separation of the cryolite for further reaction with metallic sodium but also for cryolite and sodium sale or use as products independently of the aluminum refining technique which is a disclosure of this invention.

As heretofore noted, the impure aluminum source preferably contains all three of the elements, silicon, iron and titanium. Under these circumstances at least a portion of the cryolite formed is preferably carried out of the reaction zone along with the vaporized sodium in order to more easily remove these products from residual impurities present in the reaction mixture. The aluminum-containing source should preferably contain at least 40 percent by weight of aluminum, from about 5 to about 50 percent by weight of silicon, from about 0.01 to about percent by weight of iron and from about 0.001 to about 10 percent by weight of titanium.

Reaction conditions, methods of introducing reactants and operating techniques, as well as the benefits and advantages of the invention will be more readily understood by reference to the following examples which are merely illustrative and are not intended to limit the scope of the invention.

GENERAL PROCEDURE A Vycor tube (30 mm. O.D X 300 mm.) fitted with a carbon liner (25 mm. O.D., 13 mm. ID. X 150 mm.) served as the reactor. This was attached in a vertical position to a standard high vacuum system capable of maintaining a pressure of 10' to 10" mm. Heating to l,000C was accomplished with a tube furnace. The temperature was recorded with a thermocople placed in contact with the glass and insulated from the furnace with an asbestos wrapping. A Honeywell Pyr-O-Vane was used as the temperature controller.

In the normal procedure, a weighed amount of the salt was placed into the reactor along with Al metal or alloy. The Al metal was in the form of one mm. thick sheet cut with shears to obtain the desired weight. Generally, several pieces were used, and these were inserted into the salt contained in the reaction. Alloy, when used, was added in the form of small chunks.

After charging, the reactor was attached to the vacuum system and carefully evacuated. A trap between the reactor and the pumps were cooled to -1 96C with liquid nitrogen. The reactor was then heated to the desired temperature for a predetermined length of time, after which it was cooled to room temperature.

After nitrogen was admitted to the reactor, it was removed from the vacuum line and taken into a dry box. Here it was opened and the contents removed. Generally, metallic sodium was scraped off the walls of the reactor above the heated zone and, after weighing, the sample was submitted for analysis. Any other fraction present along the walls was treated in a similar manner.

The residue left in the reactor was separated into unreacted metal and salt fractions if possible. Appropriate analyses were performed as deemed necessary.

EXAMPLE I 12.6 grams of sodium fluoride (300 mmoles) and 4 grams of aluminum alloy turnings (68% Al, 27% Si, 3% Fe and 2% Ti) (about 100 mmoles of Al) were thor oughly mixed and placed in a carbonlined Vycor reactor. The reactor was evacuated to 107 millimeters of mercury and heated slowly to 850C for 30 minutes where appreciable reaction was observed. A sodium mirror approximately 6 inches in length appeared on the sides of the reactor above the reaction mixture at this stage of the run. The reactor was then heated to 900C for 3 hours after which it was cooled and the contents removed.- 2.33 grams of sodium metal and 11.46 grams of residue consisting mostly of cryolite were recovered. Small pellets of aluminum were mixed with the cryolite. The reaction, 6 NaF alloy (Al, Si, Fe, Ti) 3 Na T Na AlF therefore took place nearly to completion, the yield of sodium metal was 67.5% based on the weight of the sodium fluoride reactam.

EXAMPLE II 7.2 grams of sodium fluoride (171 mmoles) and 4 grams of aluminum alloy (about 100 mmoles Al) having approximately the same analysis as that used in Example I were mixed and reacted in an Al O -lined Vycor reactor using the same procedures as in Example I, except that the temperature was initially adjusted to 900C. 0.79 grams of sodium and a good yield of cryolite were obtained. Small amounts of aluminum and sodium fluoride were mixed with the cryolite. This recovery corresponds to 40% yield of sodium based on the weight of the sodium-fluoride originally present. The yield based on aluminum in the alloy was poor. Sodium fluoride was not present in sufficient amount to react with all the aluminum present in the alloy.

EXAMPLE III- 12.6 grams of sodium fluoride and 4.3 grams of aluminum alloy chunks having approximately the same analysis as that used in Example I were charged into an Al O -lined Vycor reactor. The reactor was then evacuated to a pressure of 10" millimeters of mercury and heated to 900C for 4 hours, after which it was cooled. Cryolite and sodium rings were observed to be present on the reactor sides above the A1 liner. Physical separation of the cryolite and sodium from unreacted alloy and sodium fluoride was clearly observed.

The extent of reaction is strongly dependent upon the pressure of the system. At 975C little reaction occurs when the pressure is above mm. Table I hereinafter, shows the effect of pressure on the extent of the reaction.

AI ([00) Carbonlined Vycor From the foregoing it is readily seen that aluminum as the neat metal and as aluminum-silicon alloys reacts with sodium fluoride under vacuum at about 900C to form sodium metal and cryolite. Cryolite apparently forms above the heated or reaction zone.

The foregoing disclosure and description of the inventionis illustrative and explanatory thereof and various changes may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

1. A process for refining an impure aluminumcontaining source material, comprising:

a. heating the impure aluminum-containing source material with sodium fluoride in a first reaction zone to a temperature high enough to initiate reaction but below 1,000C and effecting the reaction at a reduced pressure of less than about millimeters of mercury, thereby avoiding the formation of aluminum mono fluoride and producing cryolite, residue, and metallic sodium, and causing said metallic sodium to be vaporized out of said reaction zone and separately condensed from said cryolite; and

b. reacting the cryolite produced in step (a) with metallic sodium in a second reaction zone at elevated temperature and at a pressure at least as high as normal atmospheric to keep the sodium from boiling out, thereby producing purified metallic alumi num and sodium fluoride.

2. The process of claim 1, wherein at least a portion of the cryolite formed in the first reaction zone in step (a) is vaporized out of the first reaction zone along with the vaporized sodium metal.

3. The process of claim 1, wherein said impure alumi num-containing source material contains at least 40 percent by weight of aluminum, from about 5 to about 50 percent by weight of silicon, from about 0.1 to about 40 percent by weight of iron, and from about 0.001 to about 10 percent by weight of titanium.

4. The process of claim 1, wherein said pressure in step (a) is less than about 10 millimeters of mercury.

5. The process of claim 1, wherein said temperature in step (a) is about 700C to about 1,000C.

6. The process of claim 1, wherein said temperature in step (b) is about 1,000C to about 1,300C.

7. The process of claim 1, wherein the reactions are conducted in the presence of a melting point depressant for the fluoride.

8. The process of claim 1, wherein the cryolite and residue are formed together in step (a) and then heated to melt the cryolite and then separating the molten cryolite from the residue.

9. The process of claim 1, wherein the reactions are conducted in an inert atmosphere.

it). The process of claim 1, in which the pressure in step (a) is not greater than 10' millimeters of mer- 

1. A PROCESS FOR REFINING AN IMPURE ALUMINUM-CONTAINING SOURCE MATERIAL, COMPRISING: A. HEATING THE IMPURE ALUMINUM-CONTAINING SOURCE MATERIAL WITH SODIUM FLUORIDE IN A FIRST REACTION ZONE TO A TEMPERATURE HIGH ENOUGH TO INITIATE REACTION BUT BELOW 1,000*C AND EFFECTING THE REACTION AT A REDUCED PRESSURE OF LESS THAN ABOUT 100 MILLIMETERS OF MERCURY, THEREBY AVOIDING THE FORMATION OF ALUMINUM MONO FLUORIDE AND PRODUCING CRYOLITE, RESIDUE, AND METALLIC SODIUM, AND CAUSING SAID METALLIC SODIUM TO BE VAPORIZED OUT OF SAID REACTION ZONE AND SEPARATELY CONDENSED FROM SAID CRYOLITE; AND B. REACTING THE CRYOLITE PRODUCED IN STEP (A) WITH METALLIC SODIUM IN A SECOND REACTION ZONE AT ELEVATED TEMPERATURE AND AT A PRESSURE AT LEAST AS HIGH AS NORMAL ATMOSPHERIC TO KEEP THE SODIUM FORM BOILING OUT, THEREBY PRODUCING PURIFIED METALLIC ALUMINUM AND SODIUM FLUORIDE.
 2. The process of claim 1, wherein at least a portion of the cryolite formed in the first reaction zone in step (a) is vaporized out of the first reaction zone along with the vaporized sodium metal.
 3. The process of claim 1, wherein said impure aluminum-containing source material contains at least 40 percent by weight of aluminum, from about 5 to about 50 percent by weight of silicon, from about 0.1 to about 40 percent by weight of iron, and from about 0.001 to about 10 percent by weight of titanium.
 4. The process of claim 1, wherein said pressure in step (a) is less than about 10 millimeters of mercury.
 5. The process of claim 1, wherein said temperature in step (a) is about 700*C to about 1,000*C.
 6. The process of claim 1, wherein said temperature in step (b) is about 1,000*C to about 1,300*C.
 7. The process of claim 1, wherein the reactions are conducted in the presence of a melting point depressant for the fluoride.
 8. The process of claim 1, wherein the cryolite and residue are formed together in step (a) and then heated to melt the cryolite and then separating the molten cryolite from the residue.
 9. The process of claim 1, wherein the reactions are conducted in an inert atmosphere.
 10. The process of claim 1, in which the pressure in step (a) is not greater than 10116 4 millimeters of mercury. 